The present invention relates to cultivating machines or cultivators which, though rotations of cultivating claws provided on a cultivating shaft, not only cultivate the ground but also travel in directions instructed by a human operator; such machines are commonly called xe2x80x9cfront-tine cultivators. Such cultivators are popularly used today because of their handiness and capability of making small sharp turns. Typical example of the conventionally-known cultivators is discussed below in relation to FIG. 9.
FIG. 9 is a schematic view of the conventionally-known cultivator 100, where an engine 101 capable of rotating only in one rotational direction has an output shaft 102 extending downward from the body of the engine 101. Transmission shaft 104 is coupled via a centrifugal clutch 103 to the output shaft 102, and a horizontal cultivating shaft 106 having a plurality of cultivating claws 107 is connected to the transmission shaft 104 via a worm gear mechanism 105.
The transmission shaft 104 is secured at its top to a hub 109 of an outer cup 108 of the centrifugal clutch 103 by spline coupling. The worm gear mechanism 105 includes a worm (driving gear) 111 provided on the transmission shaft 104, and a worm wheel (driven wheel) 112 provided on the cultivating shaft 106. The centrifugal clutch 103, transmission shaft 104 and worm gear mechanism 105 are together accommodated in a transmission casing 113. The transmission casing 113 supports, via a first rolling bearing 114, the outer cup hub 109 against axial displacement. Specifically, the first rolling bearing 114 has an inner race secured via a retaining ring 115 to the hub 109 against axial displacement, and an outer race secured via a retaining plate 116 and retaining screw 117 to the hub 109 against axial displacement. Further, the transmission casing 113 supports, via second and third rolling bearings 118 and 119, the transmission shaft 104 against axial displacement. Specifically, the second and third rolling bearings 118 and 119 are held against axial displacement, by means of a retaining ring 125 and stepped portions defined between the transmission shaft 104 and the worm 111 and defined in the transmission casing 113.
The transmission casing 113 has a first opening 121 formed at its lower end for insertion therein of the transmission shaft 104 and worm 111, as well as a second opening 122 formed at its side end for insertion therein of the worm wheel (driven gear) 112. After the transmission shaft 104 and worm 111 are inserted through the first opening 121 into the transmission casing 113 and fixed in place within the transmission casing 113, the first opening 121 is closed with a first lid 123. Similarly, after the worm wheel 112 is inserted through the second opening 122 into the transmission casing 113 and fixed in place within the transmission casing 113, the second opening 122 is closed with a second lid 124.
In the conventional cultivator 100 of FIG. 9, the cultivating shaft 106 and worm wheel 112 are each constructed to rotate only in a forward rotational direction R10 (counterclockwise direction in the figure), so that the worm wheel 112 would produce thrust reaction force Fs acting on the transmission shaft 104 via the worm 111 in a direction toward the centrifugal clutch 103. The thrust reaction force Fs is applied via the second rolling bearing 118 to the transmission casing 113.
However, the conventional cultivator 100 of FIG. 9, which employs the retaining ring 115, retaining plate 116 and retaining screw 117 to prevent the outer cup 24 and first rolling bearing 114 from accidentally coming off or getting disengaged from the transmission casing 113, undesirably requires a great number of necessary component parts, lowers the manufacturing (component-part-installing) efficiency and increases the necessary number of man-hours. Particularly, where the cultivator 100 is of a small size, such inconveniences would become more notable because the component parts have to be assembled and installed in a very narrow space within the small-size transmission casing 113.
Further, because the transmission casing 113 in the conventional cultivator 100 has the first and second openings 121 and 122 oriented in different directions, two separate lids 123 and 124 are required to close the respective openings 121 and 122, which further increases the number of necessary component parts, lowers the manufacturing (component-part-installing) efficiency and increases the necessary number of man-hours. Moreover, in the conventional cultivator 100, the worm 111 and worm wheel 112 are inserted into the transmission casing 113 in two different directions, which would even further lower the manufacturing (component-part-installing) efficiency. Besides, because the retaining ring 125 is employed to prevent the coming-off or disengagement, from the transmission casing 113, of the worm 111, the number of necessary component parts would increase even further.
In view of the foregoing prior art problems, it is an object of the present invention to provide a novel technique suitably applicable to a cultivator of a type where a main shaft portion of a transmission shaft, having a driving gear provided thereon, is connected, via a clutch, to an engine rotatable only in one rotational direction, and which, with a reduced number of component parts, allows the clutch and first bearing, supporting the clutch, to be efficiently installed in a transmission casing against accidental coming-off from the transmission casing.
It is another object of the present invention provide a novel technique suitably applicable to a cultivator of a type where a worm is operatively connected, via a main shaft portion of a transmission shaft, to an engine rotatable only in one rotational direction and the worm, worm wheel and main shaft portion are collectively accommodated in a transmission casing, and which, with a reduced number of component parts, allows the worm, worm wheel and main shaft portion to be efficiently installed in the transmission casing against accidental coming-off from the transmission casing.
In order to accomplish the above-mentioned objects, the present invention provides an improved cultivator which comprises: an engine capable of rotating only in one predetermined rotational direction; a transmission shaft having a driving gear provided thereon, the transmission shaft having a main shaft portion that is smaller in diameter than the driving gear and projecting from one end of the driving gear toward a clutch, the main shaft portion being operatively connected to the engine via the clutch; a cultivating shaft having cultivating claws and also having a driven gear provided thereon to meshingly engage with the driving gear; and a transmission casing having the driven gear, driving gear, main shaft portion of the transmission shaft and clutch collectively accommodated therein, the transmission casing having a first bearing for preventing the clutch from being displaced toward the driving gear and a second bearing for preventing the driving gear from being displaced toward the clutch. In the present invention, the main shaft portion of the transmission shaft is screw-coupled to the clutch and a direction in which the screw-coupling between the main shaft portion and the clutch is tightened corresponds to the one predetermined rotational direction of the engine.
The first bearing prevents the clutch from being displaced toward the worm while the second bearing prevents the worm from being displaced toward the clutch, and the main shaft portion is screw-coupled to the clutch. Thus, in the present invention, the clutch, main shaft portion and first and second bearings can be reliably prevented from displacement toward the driving gear and the driving gear can be prevented from displacement toward the clutch, with a simple structure comprising only the first and second bearings. Therefore, the present invention can eliminate the need to provide separate elements for preventing undesired displacement and disengagement, from the transmission casing, of the above-mentioned component parts. As a result, it is possible to not only reduce the number of necessary component parts but also enhance the component-part-installing efficiency, thereby minimizing the necessary number of man-hours. Furthermore, with the arrangement that the direction in which the screw-coupling between the main shaft portion and the clutch is tightened corresponds to the one rotational direction of the engine, there is no possibility of the screw-coupling gradually loosening due to the rotation of the engine.
In an embodiment of the present invention, the transmission shaft has an end shaft portion projecting from the other end of the driving gear opposite from the main shaft portion, and the end shaft portion has an adjustment section for adjusting an amount of screwing, into the clutch, of the main shaft portion of the transmission shaft. The provision of the adjustment section allows the amount of screwing, into the clutch, of the main shaft portion to be adjusted as desired with ease.
Preferably, the driving gear provided on the transmission shaft is a worm while the driven gear provided on the cultivating shaft is a worm wheel, and the transmission casing has a single insertion opening for insertion therein of the worm and worm wheel and the insertion opening is closed with a single lid. The lid constructed to also function as a member for preventing the worm from accidentally coming off or getting disengaged from the transmission casing. Thus, the present invention requires only one lid to close the insertion opening, so that it can significantly reduce the number of component parts as compared to the conventional cultivator where a plurality of insertion openings are closed with a plurality of lids. Further, because the worm and worm wheel are inserted and installed in the transmission casing in one direction, the present invention can enhance the component-part-installing efficiency. In addition, with the lid constructed to also function to prevent accidental coming-off of the worm, the present invention can eliminate the need for a separate element for preventing the coming-off of the worm. Thus, it is possible to further reduce the number of necessary component parts and enhance the component-part-installing efficiency.
Preferably, the end shaft portion of the transmission shaft is held via a third bearing within the transmission casing, and the lid is a press-formed lid integrally having a flange that is secured to an edge of the transmission casing defining the insertion opening and that supports the end surface of the third bearing. With the lid""s flange secured to the edge defining the insertion opening and also functioning to support the end surface of the third bearing to thereby prevent the third bearing from accidentally coming off the transmission casing, the present invention can eliminate the need for a separate retaining member for preventing the third bearing from coming off the transmission casing. Because the separate retaining member can be dispensed with, the present invention can even further reduce the number of necessary component parts and enhance the component-part-installing efficiency, thereby minimizing the necessary number of man-hours. In addition, the lid, simply press-formed to provide the flange, can advantageously function to reliably prevent the third bearing from accidentally coming off the transmission casing.